The present invention relates to a system for spreading liquids and other flowable materials on the ground from an aircraft.
Aircraft are widely used to fight forest and grass fires by spreading water or other fire-retardant materials on the fire. Similarly, aircraft are used to seed forests and to spread fertilizer and insecticides on agricultural crops.
One of the major factors in successfully fighting a fire is the volume of fire retardant spread over a given area. "Coverage level" is the number of gallons spread per 100 square feet. The objective is to spread enough retardant to suppress the fire without using more than is necessary.
In a simple form of airborne fire-fighting system, a container for fire retardant has one or more doors or openings which are opened to drop the entire load of retardant. Examples of that form of system are disclosed in U.S. Pat. Nos. 3,661,211 (Powers), 3,423,053 (Hawkshaw), 3,698,480 (Newton), and 3,754,601 (Linkewich), and Canadian Patent Number 709,294 (Stevenson et al).
The system described above has several disadvantages. Because the doors are opened to a constant position during the drop, the retardant flow rate decreases as the level of retardant in the container decreases. Thus, the coverage level decreases from the beginning of the drop to the end of the drop. In addition, this system does not take into account the effect of the aircraft's vertical acceleration on coverage level. If the aircraft's vertical acceleration is greater or less than one G, the coverage level will increase or decrease, respectively. This type of system also does not take into account the effect of the aircraft's speed on coverage level. As aircraft speed increases, coverage level decreases.
U.S. Pat. No. 4,936,389 (MacDonald et al) discloses a system in which the position of the container doors is varied in response to the position of a float supported on the surface of the fire retardant. The system does not, however, compensate for the aircraft's vertical acceleration or speed. Also, the system does not provide for true continuous control of the container doors, in that the float-actuated level sensor measures retardant level in discrete increments.